Police find missing Perth boy's shirt in Coober Pedy

Police have found a t-shirt that a missing Perth boy was wearing at the time of his disappearance, but forensic testing has not provided any new clues.

Police hold grave fears for three-year-old Imran Zilic, who was last seen with his father, Aalia Zilic, in Coober Pedy in South Australia's far north almost a fortnight ago.

They say the toddler was wearing the t-shirt the last time his mother saw him.

Police found the shirt in the home where Imran and his father were staying in Coober Pedy

They say the boy could still be found alive and are continuing a search of the thousands of mine shafts around Coober Pedy.

Aalia Zilic was last seen with the boy in Coober Pedy and will not divulge the boy's location to police.

He was taken to Perth on Saturday, heavily sedated and under police guard, after being detained under the Mental Health Act in Kununurra in Western Australia's north.

Charges have not been laid.

Major crime detectives from South Australia are travelling to Western Australia to speak with the father.

Detective Inspector Doug Barr says the boy's father has not cooperated with police so far.

"[The father] is in the care of the Western Australian authorities and at a time appropriate, we will make contact with him and talk to him then," he said.

"We have not charged any person in relation to the disappearance of Imran Zilic and we would encourage members of the community that we're still looking for Imran Zilic, he may well be somewhere in Coober Pedy."